GSK Pushes mRNA Flu Vaccine Into Crucial Late-Stage Trial

GSK is pushing its flu vaccine candidate into a crucial late-stage trial. The company plans to start a Phase III trial in September 2026.

The move follows positive Phase II results for its mRNA flu vaccine candidate. The vaccine produced stronger immune responses than standard-dose vaccines in younger adults. It also performed better than high-dose vaccines in older adults.

The candidate is designed to target two major surface proteins of influenza viruses. These are haemagglutinin (HA) and neuraminidase (NA).

Most existing flu vaccines mainly target HA. GSK’s approach also targets NA. The company believes this could improve protection and reduce the severity and spread of flu.

What makes GSK’s mRNA vaccine different?

GSK’s candidate is being developed as a next-generation influenza vaccine. Its design targets both HA and NA across influenza A and B strains.

Key points from the Phase II study include:

• The trial included 971 adults aged 18 years and older.
• Participants included both younger and older adults.
• The vaccine showed strong immune responses against HA and NA.
• Results were positive across all influenza strains tested.
• The safety and reactogenicity profiles were considered acceptable.
• GSK will take its optimized B-strain candidate into Phase III.

The Phase II trial, called Flu-028, assessed different doses and formulations. Participants received the investigational vaccines or licensed age-appropriate flu vaccines. GSK will now further evaluate the optimized FLUm3HA.b-3NA candidate in a Phase III efficacy trial.

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Why the Phase III trial matters

Seasonal influenza remains a major global health concern. The World Health Organization estimates that seasonal flu causes around one billion cases each year. It can also lead to up to five million cases of severe illness. Annual respiratory deaths linked to influenza can reach 650,000.

GSK received Fast Track designation from the US Food and Drug Administration (FDA) for the vaccine candidate in July 2026. The designation reflects the need for better flu protection, particularly among targeted age groups.

GSK’s Head of Vaccines and Infectious Diseases R&D, Sanjay Gurunathan, said the results support the potential of targeting both HA and NA. The company’s vaccine candidate is still investigational. It has not been approved anywhere in the world.

GSK steps up its mRNA vaccine push

The Phase III program also adds to GSK’s wider efforts to expand its vaccine pipeline. The company plans to begin the late-stage study in September. The trial would be the first Phase III study of an mRNA flu vaccine designed to target both HA and NA.

The development comes as pharmaceutical companies explore mRNA technology for seasonal influenza. Faster vaccine production is one potential advantage of the platform. However, GSK will still need to demonstrate the candidate’s efficacy and safety in the larger Phase III program.

For now, the positive Phase II results give the flu vaccine candidate a significant boost as GSK moves toward the next stage of development.